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The present invention relates to duct assemblies for use in post-tension construction. More particularly, the present invention relates to grout vents that are used to inject grout for sealing the interior of fully encapsulated post-tension construction systems.
For many years, the design of concrete structures imitated the typical steel design of column, girder and beam. With technological advances in structural concrete, however, its own form began to evolve. Concrete has the advantages of lower cost than steel, of not requiring fireproofing, and of its plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive load, is weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile forces.
Structures of reinforced concrete may be constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced-concrete framing is seemingly a quite simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size and number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, a mixture of water, cement, sand, and stone or aggregate, of proportions calculated to produce the required strength, is placed, care being taken to prevent voids or honeycombs.
One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions.
Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as one hundred feet can be attained in members as deep as three feet for roof loads. The basic principle is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principle, but the reinforcing tendon, usually a steel cable, is held loosely in place while the concrete is placed around it. The reinforcing tendon is then stretched by hydraulic jacks and securely anchored into place. Pre-stressing is done with individual members in the shop and post-tensioning as part of the structure on the site.
In a typical tendon tensioning anchor assembly used in such post-tensioning operations, there are provided anchors for anchoring the ends of the cables suspended therebetween. In the course of tensioning the cable in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of each cable for applying a predetermined amount of tension to the tendon, which extends through the anchor. When the desired amount of tension is applied to the cable, wedges, threaded nuts; or the like, are used to capture the cable at the anchor plate and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.
Multi-strand tensioning is used when forming especially long post-tensioned concrete structures, or those which must carry especially heavy loads, such as elongated concrete beams for buildings, bridges, highway overpasses, etc. Multiple axially aligned strands of cable are used in order to achieve the required compressive forces for offsetting the anticipated loads. Special multi-strand anchors are utilized, with ports for the desired number of tensioning cables. Individual cables are then strung between the anchors, tensioned and locked as described above for the conventional monofilament post-tensioning system.
As with monofilament installations, it is highly desirable to protect the tensioned steel cables from corrosive elements, such as de-icing chemicals, sea water, brackish water, and even rain water which could enter through cracks or pores in the concrete and eventually cause corrosion and loss of tension of the cables. In multi-strand applications, the cables typically are protected against exposure to corrosive elements by surrounding them with a metal duct or, more recently, with a flexible duct made of an impermeable material, such as plastic. The protective duct extends between the anchors and in surrounding relationship to the bundle of tensioning cables. Flexible duct, which typically is provided in 20 to 40 foot sections, is sealed at each end to an anchor and between adjacent sections of duct to provide a water-tight channel. Grout then may be pumped into the interior of the duct in surrounding relationship to the cables to provide further protection.
Various patents have issued, in the past, for devices relating to such multi-strand duct assemblies. For example, U.S. Pat. No. Des. 400,670, issued on Nov. 3, 1998, to the present inventor, shows a design of a duct. This duct design includes a tubular body with a plurality of corrugations extending outwardly therefrom. This tubular duct is presently manufactured and sold by General Technologies, Inc. of Stafford, Tex., the licensee of the present inventor.
This duct design has a tubular body with a plurality of corrugations which extend radially outwardly from the outer wall of the tubular body. The tubular body includes an interior passageway suitable for receiving multiple post-tension cables and strands therein. The interior passageway of the tubular body is suitable for receiving a grout material so as to maintain the multiple strands in a liquid-tight environment. The tubular body, along with the corrugations, are formed of a polymeric material. The duct can be of any length, as desired. Couplers can be used so as to secure lengths of the duct together in an end-to-end relationship.
The present inventor is also the inventor of U.S. Pat. No. 5,474,335, issued on Dec. 12, 1995. This patent describes a duct coupler for joining and sealing between adjacent sections of duct. The coupler includes a body and a flexible cantilevered section on the end of the body. This flexible cantilevered section is adapted to pass over annular protrusions on the duct. Locking rings are used to lock the flexible cantilevered sections into position so as to lock the coupler onto the duct. U.S. Pat. No. 5,762,300, issued on Jun. 9,1998, to the present inventor, describes a tendon-receiving duct support apparatus. This duct support apparatus is used for supporting a tendon-receiving duct. This support apparatus includes a cradle for receiving an exterior surface of a duct therein and a clamp connected to the cradle and extending therebelow for attachment to an underlying object. The cradle is a generally U-shaped member having a length greater than a width of the underlying object received by the clamp. The cradle and the clamp are integrally formed together of a polymeric material. The underlying object to which the clamp is connected is a chair or a rebar.
U.S. Pat. No. 5,954,373, issued on Sep. 21, 1999, to the present inventor, shows another duct coupler apparatus for use with ducts on a multi-strand post-tensioning system. The coupler includes a tubular body with an interior passageway between a first open end and a second open end. A shoulder is formed within the tubular body between the open ends. A seal is connected to the shoulder so as to form a liquid-tight seal with a duct received within one of the open ends. A compression device is hingedly connected to the tubular body for urging the duct into compressive contact with the seal. The compression device has a portion extending exterior of the tubular body.
One of the problems with these prior art systems is the ability to inject grout into the interior passageway of the duct assembly. Under certain circumstances, the grout can be injected in the areas of the couplers between adjacent lengths of duct assemblies. In other cases, the grout is injected prior to joining the ducts in end-to-end relationship. Under other circumstances, a hole is drilled into the material of the duct so as to allow a grout line to be placed into the interior of the duct assembly. Unfortunately, this process can create various obstacles to the extension of the tendons through the interior passageway of the duct assembly. Additionally, it does not establish a very secure relationship between the grout line and the wall of the duct. Often, there is a great deal of leakage. In other circumstances, the formation of any voids or holes in the wall of the tubular duct, or in the areas of the couplers, can actually allow water penetration into the interior of the duct. As a result, a need has developed so as to form a proper grout vent for such tendon-receiving ducts.
It is an object of the present invention :to provide a grout vent for a tendon-receiving duct which allows for grout to be injected into the interior passageway of the duct.
It is another object of the present invention to provide a grout vent which establishes a liquid tight seal with the duct.
It is another object of the present invention to provide a grout vent which can be easily installed through a hole formed on the body of the duct.
It is still another object of the present invention to provide a grout vent which avoids any interference with the installation of tendons through the interior passageway of the duct.
It still a further object of the present invention to provide a grout vent for a tendon-receiving duct which is easy to use, relatively inexpensive and easy to manufacture.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a grout vent for a tendon-receiving duct comprising a tubular fitting having an interior passageway, a nut secured around an exterior surface of the tubular fitting, and a sealing means extending around the tubular fitting for forming a generally liquid-tight seal with an exterior surface of the duct. The tubular fitting has a connection means at an end thereof for engaging an interior surface of the duct.
In the present invention, the nut exerts a compressive force against the sealing means at an end of the sealing means opposite the duct. The nut is threadedly engaged with the exterior surface of the tubular fitting. The sealing means comprises an annular washer compressively interposed between the nut and the exterior surface of duct. The connection means is an outwardly extending shoulder formed at the end of the tubular fitting. The shoulder has a surface for abutting the interior surface of the wall of the duct. The interior passageway of the tubular fitting is threaded. As a result, the grout line can have an end threadedly engaged with this interior passageway. The grout line will extend outwardly of the tubular fitting. The grout line has an end opening at the end of the tubular fitting so as to communicate with the interior of the duct.
The present invention is also a tendon-receiving duct having a grout vent. In the present invention, the duct is a tubular body having an interior passageway. A hole is formed through the wall of the tubular body. In particular, the tubular body has a plurality of corrugations extending radially outwardly therefrom. Each of the plurality of corrugations is in spaced relationship to an adjacent corrugation. Each of the plurality of corrugations opens to the interior passageway. In the present invention, the hole is formed on at least one of the plurality of the corrugations. In an alternative form of the present invention, the tubular body has a longitudinal channel extending between adjacent corrugations of the plurality of corrugations. In this alternative embodiment, the hole is formed on the longitudinal channel. The seal has a slot formed on an end thereof. This slot has a shape conforming to the exterior surface of the corrugation.